Filament joint for electric lamps or similar devices



y 9 0 J. w. FULTON 2,403,070

FILAMENT JOINT FOR ELECTRIC LAMPS OR SIMILAR DEVICES Filed March 1, 1945I/vvE/v m? I JDHN Fz/L'TU/v' H/s Arum/5r Patented July 2, 1946 U IiFILAMENT JOINT FOR ELECTRIC LAMPS OR DEVICES John W. Fulton, Wicklifie,Ohio, assignor to Gen eral Electric 'Jompany, a corporation oi New YorkApplication March l, 1945, Serial No. 580,318

This invention relates to filament joints, or supports and currentconnections, for filaments for electric lamps or similar devices. Thefilament mount shown and described herein is of a concentrated monoplanecoil type; but the invention is not limited to any particular type ofmount. The invention is here illustrated and explained as embodied insupports which also serve as current connections for the filament.

In filament mounts of various types, the filament or its direct supportor connector is secured to supporting members of the mount which sustaina certain amount of stress, at least part of which may from time to timebe exerted transversely of such supporting members. This attachment isusually made by methods that involve considerable heat, such as welding.In order to withstand the heat to which they are exposed during theoperation of the lamp, such supporting members are often made of metalwhich becomes very brittle where it is thus heated, such as tungsten ormolybdenum, for example. The heat also tends to embrittle the filamentat the weld. Owing to its embrittlement as described, the supportingmember becomes so weak that it may fail under the transverse or otherstresses to which it is subjected. Sometimes such a supporting membersnaps under stresses created by the mere-inertia of the supportingstructure when the lamp is subjected to a bump, either in service .orduring manufacture.

in the cases just mentioned, as also in other cases, the weld is madelaterally to a round member, giving rise to various disadvantages.

As explained more fully hereinafter, I have overcome the difliculty ofsupport embrittlement by making the supporting member of suchcrosssection (at least at the weld) that the welding heat only affectsand embrittles part of the sec-' tion, leaving another portion withsufilclent toughness and strength to withstand the transverse stresseswithout damage to the member. For this purpose, the member may include aflat, suitably wide portion at an edge of which is the part to which theweld is made, preferably to another fiat portion of the member at saidedge. To increase the resistance ofthe member under the transversestress, the first-mentioned that or wide portion or section of themember may be arranged in the plane of the transverse stress. Variousangle-sections are suitable, such as a simple angle, a channel, or a T.

I have also overcome the dimculties incident to welding laterally to around member.

Various features and advantages of the inven- 4 Claims. (Cl. 176-38)'tion will appear from the description of a species or form ofembodiment, or from the drawing.

In the drawing, Fig. 1 is a side view of a filament mount for anincandescent lamp conveniently embody ng the invention, portions of thelamp bulb being also shown; and Fig. 2 is a similar view of a filamentconnection shown in Fig. l, on a larger scale.

Fig. 3 shows a cross-section of a supporting member or side rod of themount shown in Fig. 1 with portions of the associated filament andsupport or connector, the section being taken as indicated by the lineand arrows 3-3 in Fig. 2, but on a larger scale and turned from the Fig.2 positions of the parts.

Fig. 4 is a side view corresponding to Fig, 3 illustrating the making ofthe weld and showing the welding electrodes in working relation to theparts to be welded; and Fig. 5 is a similar view at right angles to Fig.4.

The mount her illustrated is that of a projection lamp of moderately lowwattage, comprising a filament of tungsten wire coiled in a number ofupright sections 1 that are interconnected by intermediate uncoiledU-portions or blghts 2. The coils l are shown as lying all in one plane,though this is not essential. The supporting structure of the mountcomprises lead wires 3, 3 sealed through the press portion 4 of a stem 5of the lamp envelope. The leads 3, 3 are shown as bent outward at 5, 6.Long upright side extensions l, "I. o! the leads 3, 3 lie opposite andabove and below the filament 00115 I, and may consist of refractorymetal like molybdenum. As here shown, the supporting members I, 1 havetop end portions 8, 8 of ordinary metal like nickel, butt-welded to theends of the molybdenum.

,The lower ends of the rod-like supporting members I, 7 maybe bentinward and Welded to the upright portions of the leads 3, 3 and theoutbent lead portions 6, 6 may have their ends bent into hooks 9, 9which grip around or clamp the rods 1, I. The supporting structure maybe additionally braced relative to the lamp stem 5 by means oftransverse wires l0, l0 sealed into the stem (or its inward extension orarbor II) and attached to the side supports, as by welding each of saidwires in to a lead 3 between its two points of attachment to thecorresponding side member I.

For engaging and holding the filament bights 2, there are upper andlower (molybdenum) wire hooks l2, I3 whose ends are fused into the sidesof upp r and lower vitreous cross-bars or bridgerods H, IS. The upperbar H is supported by wires l6, l6 fused into its ends and welded to theend portions 8, 8 of the supporting members I, I, and the lower bar I5is supported by wires I1, I! fused into its lower ide near its ends andwelded to the lower lead portions 6, 6.

The filament is electrically connected to each lead extension I andadditionally supported therefrom by means of supporting end Portion l8of the filament, preferably with the aid of another support l9associated with said end portion I8, Fig. 2. For thi purpose, thefilament end l8 may be coiled around and welded to the support I9, whichis itself welded to the member 'I at 20. To assure that the portion ofthe filament that takes the stresses and strains shall be free ofembrittlement due to welding, the coiled filament end It is welded tothe support l9 remote from where the filament parts company with thelatter, pref erably by inclusion in the same weld 2|] that attaches thepart l9 to the member In manufacture, the filament wire may be coiled upand bent into the several sections l, ends iii, and bights 2 beforeplacing the filament on the supporting hooks l2, l3, and the spud-likesupports l9 may be inserted in the end coils ill before welding thesespuds to the members "i. To assure definite contact of the coil l8 witheach spud is and a definite length of filament in circuit be" tween thespuds, the coil Iii may be coiled to an internal size slightly smallerthan the spud it, so as to elastically grip the whole length oi thelatter in the coil.

As thus far described, the construction corre sponds to that heretoforeknown, which has been subject to the above-mentioned drawbacks arisingfrom embrittlernent of each member l at its weld 20. The inertia of theupper bar or bridge M is especially a factor in putting a strain on thebrittle side rod area at 20 when the lamp is subiected to a bump.

In accordance with my invention, I obviate these drawbacks by across-section of the member I which affords a substantial portionsuflicicntly remote from the weld not to be greatly heated when the weldis made, so that this portion remains largely or substantiallyunembi'ittlecl. I overcome the drawbacks of welding to a round member bylaterally flattening the round member I, locally, where the weld ismade. As shown in Figs. 1, 2 and 3, the member "I consists of a roundrod or wire which is deformed into a T-section at and adjacent the weld20, which involve only the flange forming the top 2| of the T, and ismade at the outer flat side of this portion 2|. Thus the flange 22forming the shank of the T in Fig. 3 is substantially unaffected by thewelding heat. and is unembrittled, so that it ofiers ample resistance totransverse stresses which might otherwise tend to snap off the member 1at the weld 20, whether during manufacture, shipment, or use of thelamp. Accordingly, the rod 1 can bend at the weld 20 without breaking,it the rod should be overstressed. As shown, this 'flange 22 isrelatively thick as compared with the top flanges 2|, 2| and extends inthe plane of transverse stress perpendicular to the common plane of thefilament lengths and of the memhers I, I, thus afiording ampleunembrittled strength. However, the flange 2|, 2|, 22 are all shownrelatively thin as compared with .the general thickness of the rod 1.

In making a weld 20 as illustrated in Figs. 3 and 4, the side rod flange22 may be accommodated in a slot of a welding electrode 22 which bearslaterally against the top flanges 2|, 2| at either side of the flange22, but has clearance around and behind said flange 22. The coiledfilament end l8 (with the support l9 already inserted therein) may beengaged in a conformative semi-circular depression of a coacting weldingelectrode 24. As shown, the parts l8, l8 extend cross-wise of the member1, at right angles thereto. When welding current i passed and theelectrodes 23, 24 are pressed toward one another, in accordance withusual spot-welding practice in the electric lamp art, the portion 2% ofthe member 1 is heated and softened, as well a the filament coil l8 andthe member it, and the parts are thu united and electrically connected.The Illament convolutions It may be embedded in the support portion 2|,and even the member is. However, the portion 22? of the member does notmake contact with the electrode and so ceives no direct heat; thereforeit remains relatively cool and retains its toughness and ductility.Indeed, this part 22 is effectively protect heating by the bearings ofthe electro: flanges 2 l, 2| at either side, which cietc path of-heating current flow throu. llanges and conduct away the heat fro Whileany suitable metals may be used for the welding electrodes M, the bestcombination seems to be one in which each electrode is of material whichis in contact with it during the welding: e. g., molybdenum for theside-rod engaging electrode 2'3, and tungsten for the ment-engagingelectrode Mi l. Such electrodes will operate satisfactorily for thewelding of some hundreds of joints before their acting ends needreshaping.

It will be seen that while the area of molybdcnum to which the filamentl is welded is made brittle to about the same degree as in priorpractice, the flat surface at Ill to which the filament coil I8 islaterally welded is considerably larger than the area of round rod towhich the filament is welded in ordinary practice, so that the totalstrength of the joint is enough to keep the filament from breakingloose. Moreover, the fiat surface at 2| does not tend to spread apartthe brittle filament convolutions and break them when the parts arepressed together during welding, as the round rod surface does inordinary practice. On the contrary, the weld includes several turns ofthe filament coil all laterally adherent to the flat surface at 2 l Thethin molybdenum section distorts somewhat during welding, which affordsan indication of the depth of fusion of the part 2| during welding;whereas a weld to a round rod affords no such indication, Furthermore,the weld can be made just as well for any angle between the side rod 1and the spud 9 and coil l8, as seen in Fig. 2, within a considerablerange of variation; whereas in welding to a round rod, the spud tendstoassume an angle corresponding to the pitch of the coil. This latitudetakes care of variations in the angle of coil l8 to coils without anytendency to bending or straining the filament between the coils and I8.In making the welds, the electrode 23 may be allowed to rotate about itsown vertical axis, so as to accommodate itself to whatever the angle ofthe parts 1, l8, It may happen to be in each particular case.

.What I claim as new and desire to secure by Letters Patent of theUnited States is:

1. In a filament mount, the combination of a supporting upright that issubject to transverse stress and is embrittled by welding, said uprightembodying an intermediate portionthat is thin and wide in a plane oftransverse stress and has a welding portion extending laterally from anedge oi the wide portion, and a filament support welded to the side ofsaid laterally extending welding portion.

2. In a filament mount, the combination of a supporting rod that issubject to transverse stress and is embrittled by welding, said rod'having an intermediate portion deformed into an angle I lar devicescomprising a supporting rod of ductile metal which is embrlttled bywelding, said rod having a localized portion deformed into a T- shapedcross-section, and a metallic filament having an end portion extendingtransversely of the rod across the head of said T-shap d portion andwelded thereto, the stem of said T-shap d portion being comparativelyductile.

4. In a filament connection, the combination witha round support rodlaterally flattened locally, of a multi-turn wire coil extending acrossthe surface of the locally flattened portion of said rod at an angletothe rod and having the sides of its convolutions welded to saidsurface.

JOHN W. FULTON.

